This is a study of the impact of aerobic exercise conditioning on blood pressure variability (BPV) responses to psychological and physical stressors. It derives from a model which holds that autonomic control of the heart serves a buffering or inhibitory function over oscillations in blood pressure, which recent research in vascular biology and dynamics suggests may have pathogenic effects on the endothelium, in the case of atherogenesis, and on plaque stability, in the case of catastrophic cardiac events. Moreover, BPV appears to be a risk factor for cardiovascular disease independent of mean arterial pressure. This model suggests that increasing autonomic control of the heart, as measured by heart period variability (HPV), will result in reduced BPV responses to challenge. These findings suggest that one mechanism by which physical exercise promotes reduced risk of heart disease may be through the dampening of BPV responses to challenge and that this dampening is a function of the degree of HPV. This study will test this model in longitudinal study of the effect of aerobic conditioning on BPV responses to challenge and during 24-hour ambulatory BP monitoring, using U.S. Army ROTC students. In this study, sedentary ROTC recruits will be tested for BPV responses to challenge and 24-hour ambulatory BPV both before and after random assignment to either 1) a 16 week program of aerobic conditioning or 2) a 16 week program of strength training only. After the post-training set of tests, all subjects will undergo a period of deconditioning after which they again will be tested. A series of hypotheses will test the impact of aerobic conditioning on autonomic control of the heart, BPV responses to challenge, mood, and BPV throughout the day.